A test method for verifying differential circuit by replacing primary current with initial load of grid connection

Abstract

A test method for replacing a primary current to verify a differential circuit by an initial load connected to a grid relates to the technical field of power system verification. In order to solve the problem of primary current verification and determine the correctness of the differential circuit wiring, the test duration of the prior art is as long as more than 4 hours, and a large amount of power resources need to be consumed to maintain the test conditions, which is very costly and may cause delayed grid connection. The present invention calculates the action characteristics of differential protection of components, designs action curves a, b and c according to the data, and compares and analyzes whether the wiring is correct based on the data with the action curves a, b and c. Under the premise of not affecting the safe and stable operation of the unit, and without the need for large current test equipment, the test of the differential circuit of the primary current verification generator-transformer group protection system is completed efficiently and at zero cost, saving power resource costs and solving the technical problems in the industry.

Description

Technical Field

[0001] The invention relates to the technical field of power system verification, and in particular to a test method for verifying a differential circuit by replacing a primary current with a grid-connected initial load. Background Art

[0002] When the generator-transformer protection device of a power plant is newly installed or the circuit has undergone major changes, before the first grid-connected operation, the verification procedure clearly requires that the primary current must be used to verify and determine the correctness of the differential circuit wiring. Due to the large electrical capacity of the generator-transformer system, the required primary current is at least 1000A-2000A per phase. It is almost impossible to find such test equipment and it is impossible to verify whether the characteristics of the current transformer itself are normal. The general practice is to select multiple appropriate short-circuit points and conduct short-circuit tests on the generator-transformer group one by one. The test lasts for more than 4 hours. Maintaining the test conditions consumes a lot of power resources (coal, water, etc.), the cost is very high, and it may cause delayed grid connection. In the absence of high-current test equipment, how to use primary current to verify the correctness of the differential circuit wiring at low cost and high efficiency is a technical problem that the industry urgently needs to solve. Summary of the invention

[0003] The present invention provides a test method for verifying a differential circuit by replacing a primary current with an initial grid-connected load, which can realize direct grid connection of a generator-transformer group protection device after a new installation or renovation, without the need for a generator-transformer group short-circuit test. The initial load is used to replace the primary current, and the correctness of the differential circuit wiring is verified by reasonably setting the differential protection setting and adjusting the operating mode, under the premise that the generator-transformer group protection device does not malfunction or refuse to operate.

[0004] The present invention provides a test method for replacing a primary current with a grid-connected initial load to verify a differential circuit, comprising the following steps:

[0005] Step 1: Draw the action curve a according to the action characteristics of the component differential protection;

[0006] Step 2: Under the condition of correct polarity, calculate the differential protection action value corresponding to different load currents and draw the action curve b;

[0007] Step 3: In the case of reverse polarity, calculate the differential protection action values ​​corresponding to different load currents and draw the action curve c;

[0008] Step 4: Find the minimum operating current Is of the differential protection and the minimum operating current value Imin corresponding to 10%Ie rated current on the operating curve b;

[0009] Step 5: If Is>Imin, go to step 7;

[0010] Step 6: If Is < Imin, temporarily set the minimum operating current Is of the differential protection to the minimum operating current value Imin corresponding to 10% of the rated current Ie.

[0011] Step 7: In the initial stage of grid connection, collect the current values and phases on each side of the differential protection, calculate the differential current value and restraint value according to the formula, and compare them with the operating curve b and operating curve c. If it is close to the operating curve b, execute Step 9; if it is close to the operating curve c, adjust the internal CT polarity control word in the dedicated software used or correct the secondary circuit.

[0012] Step 8: Restore the temporarily set minimum operating current value Is. If there is no modification, skip it.

[0013] Step 9: Gradually increase the load to the stable state according to the normal start-stop operation, and still be connected by the start-up and standby transformer.

[0014] Step 10: After vacating the branch of the plant high-voltage transformer or the common transformer to receive the bus section, switch the plant power supply, and switch the empty bus section connected by the start-up and standby transformer to the branch of the plant high-voltage transformer or the common transformer to connect.

[0015] Step 11: Select any one or more high-voltage motors on the bus section connected by the vacated branch of the plant high-voltage transformer or the common transformer, and directly verify with the load current simulating the primary current. If there is no differential current, it proves that the wiring is correct.

[0016] Step 12: If there is differential current, adjust the internal CT polarity control word in the dedicated software used in supporting or correct the secondary circuit.

[0017] When the polarity control word adjustment is that the internal control word of the software is set to 0, the polarity remains unchanged; when it is set to 1, the polarity is automatically reversed.

[0018] Advantages of the present invention: After executing all steps of the test method for verifying the differential circuit of the initial grid connection load replacing the primary current of the present invention, without affecting the safe and stable operation of the unit, without the need for large current test equipment, the test of the differential circuit of the generator-transformer unit protection system is completed efficiently and at zero cost, saving the power resource cost and solving the technical problems in the industry. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 It is a schematic diagram of Curve a of the present invention;

[0020] Figure 2 It is a schematic diagram of Curve b of the present invention;

[0021] Figure 3 It is a schematic diagram of Curve c of the present invention;

[0022] Figure 4 It is the main wiring diagram of the generator-transformer unit system of the present invention

[0023] Figure 5 Schematic diagram of the process of the present invention; Specific embodiments

[0024] The present invention is applicable to the occasion where, when a new installation of the generator-transformer unit protection device in a power plant or when the circuit has a large change and is first connected to the grid, it is necessary to use primary current to verify and determine the correctness of the differential circuit wiring.

[0025] Such as Figure 5 As shown: A test method for replacing primary current with initial load during grid connection to verify the differential circuit of the present invention, the test method includes the following steps:

[0026] Step 1: According to the operating characteristics of the element differential protection, draw the operating curve a;

[0027] Step 2: Under the condition of correct polarity, calculate the operating values of the differential protection corresponding to different load currents, and draw the operating curve b;

[0028] Step 3: Under the condition of reverse polarity connection, calculate the operating values of the differential protection corresponding to different load currents, and draw the operating curve c;

[0029] Step 4: Find the minimum operating current Is of the differential protection and the minimum operating current value Imin corresponding to 10% Ie rated current on the operating curve b;

[0030] Step 5: If Is > Imin, then execute Step 7;

[0031] Step 6: If Is < Imin, then temporarily set the minimum operating current Is of the differential protection to the minimum operating current value Imin corresponding to 10% Ie rated current;

[0032] Step 7: In the initial stage of grid connection, collect the phase and amplitude of the currents on each side of the differential protection, calculate the differential current value and braking value, and compare them with the operating curve b and the operating curve c. If it is close to the operating curve b, then execute Step 9; if it is close to the operating curve c, then adjust the internal CT polarity control word in the dedicated software used or correct the secondary circuit;

[0033] Step 8: Restore the temporarily set minimum operating current value Is, and skip it if there is no modification.

[0034] Step 9: Gradually increase the load to the stable state according to the normal start-stop operation, and still be connected by the start-up and standby transformer;

[0035] Step 10: After evacuating the plant high-voltage transformer branch or the common transformer to receive the bus section, switch the plant power supply, and switch the empty bus section connected by the start-up and standby transformer to the plant high-voltage transformer branch or the common transformer to connect;

[0036] Step 11: Select any one or more high-voltage motors on the vacated plant high-voltage transformer branch or public transformer busbar, and use the load current to simulate the primary current for direct verification. If there is no differential current, it proves that the wiring is correct;

[0037] Step 12: If there is a differential current, use the internal CT polarity control word adjustment in the supporting dedicated software or correct the secondary circuit.

[0038] The polarity control word is adjusted so that when the internal control word of the software is set to 0, the polarity remains unchanged, and when it is set to 1, the polarity is automatically reversed.

[0039] The following is attached Figures 1 to 5 The test method of replacing the primary current to calibrate the differential circuit by the initial load of the grid is further described in detail through an embodiment.

[0040] Example: The protection of the generator-transformer system of a power plant adopts variable slope ratio differential, and the action characteristic equation is:

[0041]

[0042]

[0043] Where Id is the differential current, Ir is the braking current, Is is the differential current starting value (minimum operating current), and Ie is the rated current;

[0044] For the generator transformer differential, I1, I2, and I3 are the transformer high-voltage side bushing TA current, generator neutral point, and plant transformer high-voltage side current, respectively, and I4 is undefined;

[0045] For the main transformer differential, I1, I2, I3, and I4 are the currents on the transformer high voltage side I, II, generator end, and plant transformer high voltage side respectively;

[0046] For the high-voltage transformer differential, I1, I2, and I3 are the A and B branch currents on the high-voltage side and low-voltage side of the high-voltage transformer, respectively, and I4 is undefined;

[0047] Ratio braking coefficient definition:

[0048] Kbl is the ratio differential braking coefficient, Kb1r is the ratio differential braking coefficient increment;

[0049] Kb11 is the initial ratio differential braking coefficient, which is generally taken as 0.1;

[0050] Kb12 is the maximum ratio differential braking coefficient, which is generally taken as 0.7;

[0051] n is the braking current multiple at the maximum ratio braking coefficient, which is fixed at 6.

[0052] Table 1: Data Table of Load at the Initial Stage of Grid Connection of 600MW Steam Turbine Generator

[0053]

[0054]

[0055] Step 1: Query the setting value of the generator differential protection device: n is fixed at 4, the rated secondary current is 3.5A (Ie), the starting slope S1 = 0.1, the maximum slope S2 = 0.5, and the minimum operating current Is = 1.05A (0.3Ie). Draw the operating curve a according to the operating equation.

[0056] Step 2: Calculate the actual differential current generated by the relevant current circuits of the generator differential protection under the conditions of 1.1%, 1.2%, 1.3%, …… 10% Ie of the rated current Ie and with the correct polarity, which is 0. Calculate the corresponding differential protection operating value and draw it on the operating curve b.

[0057] Step 3: According to the analysis of historical measured data, within 7 minutes after the first grid connection of the generator-transformer unit system, the power of each component (taking the 600MW steam turbine generator as an example) generally does not exceed 5% of the rated capacity. During this period, the current of each component generally fluctuates within the range of 1% Ie - 10% Ie of the rated current. As shown in Table 1, calculate the actual differential current (2 times the measured current) generated by the relevant current circuits of the generator differential protection under the conditions of 1.1%, 1.2%, 1.3%, …… 10% Ie of the rated current Ie and with the reverse polarity, and the corresponding differential protection operating value, and draw it on the operating curve c.

[0058] Step 4: Compare the generator operating curve b and the operating curve c, find the minimum operating current value Imin corresponding to 10% Ie of the rated current, and compare it with the minimum operating current Is of the generator differential protection. If Imin > Is, then temporarily set it as the minimum operating current value Imin corresponding to 10% Ie of the rated current; if Imin < Is, then there is no need to modify the setting value. In this case, from the operating curve b and the operating curve c, it is obvious that Imin < Is, so there is no need to modify the differential protection setting value. And within 7 minutes at the initial stage of grid connection, compare the sampled values of the generator current amplitude, phase, differential current value, braking value, etc. with the operating curve b and the operating curve c. If it is incorrect, adjust it using the internal CT polarity control word in the supporting special software. If it is correct, then proceed to Step 5.

[0059] Step 5: After confirming that the wiring of the generator differential current circuit is correct, continue to check the wiring of the differential-related current circuits of other components (such as the main transformer, etc.). After confirming that all are correct, restore the modified setting value (the minimum operating current Is of the differential protection). The load can be gradually increased to the stable state according to the normal start-stop operation, but the plant power system cannot be switched, and it is still powered by the start-up and standby transformer.

[0060] Step 6: As attached Figure 1 As shown, all loads of the plant high-voltage transformer A branch (6kV working section A) are adjusted to the plant high-voltage transformer B branch (6kV working section B). After the 6kV working section A bus section is vacated, the plant power is switched with a fast switching device, and the 6kV working section A empty bus of the standby transformer is switched to the plant high-voltage transformer A branch.

[0061] Step 7: Since the 6kV working section A is an empty busbar, and all loads that affect the operation of the unit have been transferred to the 6kV working section B connected by the standby transformer, even if the branch busbar protection is activated, it will not affect the safe operation of the unit. At this time, there is no need to modify the protection setting value, and a current verification test can be carried out.

[0062] Step 8: According to the actual load current, select one or more high-voltage motors connected to the 6kV working section A, and use the load current to simulate the primary current to directly verify the correctness of the wiring of the plant high-voltage transformer A branch differential protection circuit. If there is a differential current, use the internal CT polarity control word in the matching special software to adjust it. If there is no differential current, it proves that the wiring is correct.

[0063] Step 9: Similarly, adjust all loads of the plant high-voltage transformer B branch (6kV working section B) to the plant high-voltage transformer A branch (6kV working section A), vacate the 6kV working section B bus section, use the fast switching device to switch the plant power supply, and switch the 6kV working section B empty bus of the standby transformer to the plant high-voltage transformer B branch.

[0064] Step 10: According to the actual load current, select one or more high-voltage motors connected to the 6kV working section B, and use the load current to simulate the primary current to directly verify the correctness of the wiring of the plant high-voltage transformer B branch differential protection circuit. If there is a differential current, use the internal CT polarity control word in the supporting special software to adjust it. If there is no differential current, it proves that the wiring is correct.

[0065] Step 11: Similarly, adjust all loads of the #1 high-voltage transformer branch (6kV public B section) to the #2 high-voltage transformer branch (6kV public A section), vacate the 6kV public B section bus section, use the fast switching device to switch the factory power, and switch the 6kV public B section empty bus of the standby transformer to the #1 high-voltage transformer branch.

[0066] Step 12: According to the actual load current, select one or more high-voltage motors connected to the 6kV common B section, and use the load current to simulate the primary current to directly verify the correctness of the wiring of the high-voltage transformer branch differential protection circuit. If there is a differential current, use the internal CT polarity control in the matching special software to adjust it. If there is no differential current, it proves that the wiring is correct.

[0067] The principles of other components of the generator-transformer system (main transformer, etc.) are the same as above and will not be listed one by one.

[0068] The above is only a specific implementation of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by a technician familiar with the field within the technical scope disclosed in the present invention should be covered by the protection scope of the present invention.

Claims

1. A test method for replacing the primary current to calibrate the differential circuit with the initial grid-connected load, characterized in that: The test method includes the following steps: Step 1: Draw the action curve a according to the action characteristics of the component differential protection; Step 2: Calculate the action values of the differential protection corresponding to different load currents and draw the action curve b under the condition of correct polarity; Step 3: Calculate the action values of the differential protection corresponding to different load currents and draw the action curve c under the condition of reverse polarity; both the action curve a, the action curve b, and the action curve c represent curves with the vertical axis being Id / Ie and the horizontal axis being Ir / Ie, where Id is the differential current, Ir is the braking current, and Ie is the rated current; Step 4: Find the minimum operating current Is of the differential protection and the minimum operating current value Imin corresponding to 10%Ie rated current on the action curve b; Step 5: If Is > Imin, then execute Step 7; Step 6: If Is < Imin, then temporarily set the minimum operating current Is of the differential protection to the minimum operating current value Imin corresponding to 10%Ie rated current; Step 7: In the initial stage of grid connection, collect the phase and amplitude of the currents on each side of the differential protection, calculate the differential current value and the braking value, and compare them with the action curve b and the action curve c. If it is close to the action curve b, then execute Step 9; if it is close to the action curve c, then adjust the internal CT polarity control word in the supporting special software or correct the secondary circuit; Step 8: Restore the temporarily set minimum operating current Is of the differential protection. If the minimum operating current Is of the differential protection is not modified, skip it; Step 9: Gradually increase the load to the stable state according to the normal start-stop operation, and still be connected by the start-up and standby transformer; Step 10: After vacating the plant high-voltage transformer branch or the common transformer to receive the bus section, switch the plant power supply, and switch the empty bus section connected by the start-up and standby transformer to the plant high-voltage transformer branch or the common transformer to connect; Step 11: Select any one or more high-voltage motors on the bus section connected by the vacated plant high-voltage transformer branch or the common transformer, and directly calibrate with the load current simulating the primary current. If there is no differential current, it proves that the wiring is correct; Step 12: If there is differential current, then adjust the internal CT polarity control word in the supporting special software or correct the secondary circuit; The adjustment of the polarity control word is that when the internal control word of the supporting special software is set to 0, the polarity remains unchanged, and when it is set to 1, the polarity is automatically reversed.

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